The U.S. Department of Energy's Oak Ridge Leadership Computing Facility and its Jaguar system kept the No. 1 spot on the Top500 list of fastest supercomputers, but China's new Nebulae is close behind at No. 2.

The Top500 list was presented June 31 at the ISC'10 Conference held in Hamburg, Germany. The rankings are compiled by Hans Meuer of the University of Mannheim, Germany; Erich Strohmaier and Horst Simon of NERSC/Lawrence Berkeley National Laboratory; and Jack Dongarra of the University of Tennessee, Knoxville.

Nebulae, which emerged late last year as China's big entry into supercomputing, is currently the fastest system worldwide with a theoretical peak performance of 2.98 petaflops per second. One petaflop/s is one quadrillon calculations per second.

Nebulae, located at the National Supercomputing Centre in Shenzhen, China, runs on a Dawning TC3600 Blade system with Intel X5650 processors and Nvidia Tesla C2050 GPUs. Nebulae's Linpack performance benchmark was 1.271 PFlop/s so it was No. 2. Dawning is an Asia-based high performance computing vendor. Supercomputing systems with GPU accelerators have a higher theoretical limit.

Jaguar held on to No. 1 with 1.75 PFlop/s. Jaguar's theoretical peak is 2.3 Pflop/s and almost a quarter of a million cores.